If he had a high pressure leak the system would retain gas when not operating, once the pressure normalized below the pressure the leak was susceptible to. Putting more gas in to see if anything changes is a good route to go, but if the hissing gets louder or the High/Low values go out of range then it is time to do what Agent X recommended and put a Vac pump on and see if it holds. After a vacuum is pulled, give it at least 30 min to see if it holds. In the years I worked doing A/C repair I never heard one hiss in normal operation, but then my work was in the period where R-12 was the automotive refrigerant. Maybe 134 is different.
17:48:03 05/19/23
